I crushed my grapes in late September & squeezed them. Then racked it 2 times since then. It’s been almost 2 months since the last racking and 1 of the 5 gallon wine carboys is starting to bubble again just slightly. What is happening should I do anything. The other 3 carboys are not doing this???
It’s hard to know exactly what is going on with your forth carboy, but here are your possibilities:
1) Your wine has started to ferment again: This means that the original fermentation did not consume all the original sugars before it stopped. This is known as a stuck fermentation. You can verify this, or rule it out, by taking a reading with a gravity hydrometer.
If the reading on the specific gravity scale reads .998 or higher, then there are still some sugars to be fermented. Your best course of action would be to make sure the wine carboys are not too cold, at least 70F., and wait until all the sugars are fermented.
2) You added more sugar after the fermentation: If you added more sugar to sweeten the wine after the fermentation completed but did not add a wine stabilizer along with the sugar, you are in the same situation as before. The wine has started to ferment again. The only thing that you can really do at this point is to let the wine finish out the fermentation with the newly added sugars.
If you want a sweet wine, add sugar again, after the fermentation. Only this time also add Potassium Sorbate along with the sugar. This will inhibit the fermentation from restarting.
3) Your wine has become infected with a bacteria: This may be the case if you take a reading with a gravity hydrometer and it does not indicate that there are any sugars left in the wine carboy. This does not necessarily mean it is ruined, but it needs to be addressed.
Bacterial infection is something that normally happens when sulfites such as Campden Tablets or Potassium Metabisulfite are not used after the fermentation. In any event, the problem is easily rectified by adding a dose of either of these to destroy the bacteria.
Hope this helps you out.
Happy Wine Making,
Ed Kraus is a 3rd generation home brewer/winemaker and has been an owner of E. C. Kraus since 1999. He has been helping individuals make better wine and beer for over 25 years.